1. Field of the Invention
The invention relates in general to pulse wheel systems, and more specifically to pulse wheel systems which generate first and second pulse trains having a predetermined phase shift between them, in response to rotation of a pulse wheel.
2. Description of the Prior Art
Pulse wheel systems may be used to develop first and second pulse trains which are processed to determine travel direction and distance traveled of a predetermined object, such as an elevator car. Speed of travel may also be determined from the pulses, if desired. In the prior art, two photoemitter-photodetector pairs are mounted on a mounting block and the mounting block is positioned relative to the teeth of a pulse wheel to enable the detector pairs to each develop a pulse train. In order to develop accurate information from the pulse trains, the pulse trains must have a 90 degrees phase difference between them. Since the adjustment of the detector mounting block is a three-axis adjustment which is made while the pulse wheel is rotating, it is difficult and time-consuming to make the adjustment, and extreme care must be taken to avoid the moving teeth of the pulse wheel. An oscilloscope or brush recorder is usually connected to receive the two pulse trains, and the detector mounting block is adjusted until the instrument shows that the pulse trains have equal on-off times and the desired phase shift.